As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for secondary batteries has also sharply increased. Among such secondary batteries is a lithium secondary battery exhibiting high energy density and operating voltage and excellent preservation and service-life characteristics, which has been widely used as an energy source for various electronic products as well as for the mobile devices.
However, various combustible materials are contained in the lithium secondary battery. As a result, there is a possibility of danger in that the lithium secondary battery will be heated or explode due to overcharge, overcurrent or any other external physical impacts. In other words, the lithium secondary battery has low safety. Consequently, safety elements, such as a positive temperature coefficient (PTC) element and a protection circuit module (PCM), to effectively control an abnormal state of the lithium secondary battery, such as overcharge or overcurrent, are mounted in the lithium secondary battery in a state in which the safety elements are connected to a battery cell of the lithium secondary battery.
Generally, the PCM is connected to the battery cell via conductive nickel plates by welding or soldering. That is, nickel plates are connected to electrode tabs of the PCM by welding or soldering, and then the nickel plates are connected to electrode terminals of the battery cell by welding or soldering. In this way, the PCM is connected to the battery cell, thereby manufacturing a battery pack.
It is necessary for safety elements, including such a PCM, to be maintained in electrical connection with electrode terminals of a battery cell and, at the same time, to be electrically isolated from other parts of the battery cell. A plurality of insulative mounting members or a plurality of parts is necessary to achieve such connection with the result that a process for assembling a battery pack is complicated, and the size of a space to receive the battery cell is reduced.
Also, a plurality of welding or soldering processes is required to constitute a battery pack. Such welding processes must be carried out with high precision because the structure of the secondary battery is very small with the result that a defect ratio may be increased. Furthermore, such processes are added to manufacture a product with the result that manufacturing cost of the product is increased.
For this reason, research has been actively conducted on technology to reduce the number of parts to be mounted to the top of the battery cell and simplify the assembly process of the battery cell, thereby improving manufacturing efficiency of the battery cell. For example, Korean Patent Application Publication No. 2007-01566 discloses a lithium secondary battery including a protection circuit unit having a protection circuit, the protection circuit unit including a cathode terminal and an anode terminal, a bare cell including an electrode assembly, a container in which the electrode assembly is mounted, and a cap assembly to seal the container, the cap assembly having a cap plate formed at one side thereof, the cap plate being provided with an electrolyte injection port, and a cathode lead plate and an anode lead plate to electrically connect the bare cell and the protection circuit unit to each other, wherein a protruding part is formed at the cathode lead plate, and the protruding part of the cathode lead plate is inserted into the electrolyte injection port during manufacturing of the battery so as to prevent the protection circuit unit from being separated from the bare cell.
In the above technology, however, it is complicate to manufacture the cathode lead plate configured in a specific structure having the protruding part. Also, the protruding part serves to seal the electrolyte injection port. However, it is not possible to prevent leakage of an electrolyte through only the forcible insertion of the protruding part. The electrolyte injection port may be sealed by welding the protruding part to the electrolyte injection port so as to prevent the leakage of the electrolyte. In this method, however, such an additional process is required, and therefore, manufacturing efficiency is lowered.
Consequently, there is a high necessity for technology to reduce the number of members mounted to the top of the battery cell, thereby simplifying an assembly process, to eliminate a welding process, thereby minimizing a defect ratio during the assembly of battery cells, and to achieve stable coupling between members disposed at the top of the battery cell.